private void updateVar(SetVar v) throws ContradictionException {
   if (!v.isInDomainEnveloppe(s)) {
     v.remFromEnveloppe(t, this, true);
   } else {
     v.addToKernel(s, this, true);
   }
 }
 @Override
 public String pretty() {
   StringBuilder sb = new StringBuilder();
   sb.append("ValuePrecede(" + s + "," + t + ",{");
   for (int i = 0; i < vars.length; i++) {
     if (i > 0) sb.append(", ");
     SetVar var = vars[i];
     sb.append(var.pretty());
   }
   sb.append("})");
   return sb.toString();
 }
 private boolean checkKerEnv(SetVar v) {
   return !v.isInDomainEnveloppe(s) || v.isInDomainKernel(t);
 }